Skin pigmentation disorders are conditions that cause the skin colour to appear lighter or darker than normal. The principal determinant of skin colour is the melanin pigment and variation in the amount and distribution of melanin in the skin are the basis of the three principal skin colours namely black, brown and white. Abnormality of melanin production causes skin pigmentation disorders.
There are two main categories of skin pigmentation disorders namely hypo-pigmentation and hyper-pigmentation. Hypo-pigmentation is the loss of skin colour caused by melanin depletion whilst hyper-pigmentation is the darkening of area of skin caused by increased melanin. Albinism and vitiligo are examples of hypo-pigmentation and melasma and freckles are examples of hyper-pigmentation. Hypo-pigmentation may be caused by melanocyte production being impaired for instance in a serious accident where most of the pigment producing layers of the upper skin would be damaged. Melanocytes make melanin, the pigment that gives the skin its color. If melanocytes production is impaired, so is the skin's ability to produce darker skin tones. Hy per-pigmentation may be caused by sun damage, inflamation or other skin injuries. Current treatment for hypo-pigmentation is typically carried out by various methods such as photochemotheraphy, topical corticosteroids, topical immuno-modulators, synthetic vitamin D3 analogues, therapy and a plethora of surgical techniques. Current treatment for hyper-pigmentation on the other hand is by bleaching and photochemotheraphy. In order to alleviate health risks associated to invasive treatments, tools for measuring melanin and other pigment levels that have been introduced and developed to treat skin pigmentation disorders have the tendency to be non-invasive in nature. Amongst such non-invasive measurement tools are namely camera to capture RGB image (Takiwaki et al 1994; Takiwaki et al 1998, Jung et al 2004); Chromameter to obtain colour data (P. Clarys et al 2001; Alaluf et al 2002, Nayan et al 2008), Derma spectrometer to obtain colour data (P. Clarys et al 2001; Lieneke et al 2003), Multispectral camera to capture multispectral image (Moncrieff et al 2002, Luadi et al 2006, Bushra J. 2008).
In the above non-invasive treatment, changes to the skin surface colour as a response to treatment takes time. To assess the efficacy of different treatment modalities of skin pigmentation disorder, a considerable time is needed for skin surface colour to change. This is because the measurement process (under Physician's Global Assessment [PGA] framework) only refers to the visual conditions of the skin surface and does not assess the conditions of the underlying skin layers and pigments. Moreover the PGA protocol is not yet standardised.
Hence the delay caused by observing the changes to the skin surface colour as a response to treatment is not an effective solution and a better more effective method has to be researched upon. It has been known that there are two types of melanin namely eumelanin and pheomelanin which are important in the understanding of the underlying causes of skin pigmentation disorders which would greatly facilitate analysis of pigmentation disorder reliably. Eumelanin is found in people with dark skin and gives a black or brown colour whilst pheomelanin is found in people with light and dark skin and gives a red and yellow colour [Thody A. J et al. 1991]. From the above literature, although there are many non-invasive tools for measuring skin pigments, there is currently no validated in vivo method that is non-ionising and non-invasive to accurately measure melanin types and quantities to be used in assessing severity of skin pigmentation disorder and treatment efficacies. There is presently no known methods and devices to classify and determine the types of melanin namely eumelanin and pheomelanin save for the biochemical method [A. J. Thody et al 1991; Ito 2003] which is unfortunately invasive in nature as skin biopsy is conducted for chemical analysis of skin samples. This biochemical method is able to classify and measure the types of melanin (eumelanin and pheomelanin) which is important in understanding the underlying causes of skin pigmentation disorder but being invasive in nature would carry with it certain health risks or perhaps discomfort, no matter how minor the treatment is.
The tools for measuring melanin and other pigment levels enables quantification of the level of the melanin pigment types in the skin but it would not be of assistance in analysing the severity of skin pigmentation disorder. For this reason skin pigmentation models are developed not only to give a detailed understanding on the role of melanin pigment types in human skin but also to develop an objective method for the classification of melanin pigment types in human skin. Present skin pigmentation models for analysing skin have revolved around analysing the skin dermis solely; the skin dermis together with epidermis; the skin dermis together with the epidermis and skin pigment (melanin); the skin dermis, together with epidermis and skin pigment (melanin and other pigments). Skin pigmentation models for analysing the skin dermis solely are the Empirical (Kulbelka Munk) model disclosed by Anderson et al 1981 and the Simulated (Monte Carlo) model by Prahl et al 1989. Skin pigmentation models for analysing the skin dermis together with epidermis are the Empirical (Kulbelka Munk) model disclosed by, Wan et al 1981 and Diffey et al 1983 and the Simulated (Monte Carlo) model by Wang et al 1995. Skin pigmentation models for analysing the skin dermis together with epidermis and skin pigment (melanin) are the Empirical (Kulbelka Munk) model disclosed by Cotton et al 1996, Cotton et al 1997. Skin pigmentation models for analysing the skin dermis together with epidermis and skin pigment (melanin and other pigments) are the Empirical (Kulbelka Munk) model as disclosed by Do et al 2003; the Simulated (Monte Carlo) model disclosed by Tsumura et al 2000, Meglinsky et al 2001, Shimada et al 2003 and Meglinsky et al 2007; and the Statistical (ICA) model by Tsumura et al 1999, Tsumura et al 2004 and Fadzil et al 2009. However to date there are no new skin pigmentation models that can analyse skin dermis epidermis as well as the melanin pigment types namely eumelanin and pheomelanin which as is known is vital in providing valuable information on the condition of skin enabling reliable analysis on the severity of skin pigmentation disorder for proper and expedited treatment.
It would hence be extremely advantageous if the above shortcoming is alleviated by having a non-invasive method for determining the level of the melanin types namely eumelanin and pheomelanin in order to facilitate the developing of human skin pigmentation computation model using digital signal and image analysis of hyperspectral sensing and multispectral data.